Rubber compositions and process of producing same



Patented July 4, 1950 I RUBBERCOMBOSITIONS AND PROCESS OF PRODUCING SAME Joseph C'.'Ambel'ang, Akron, Ohio; assignor'to The; Firestone Tire& Rubber Company; Akron, Ohio, a corporation of Ohio No Drawing. Application October Serial-No. 732,943,

invention relates to naturalrubber compositions which contain antiflex-crackingagents. These antifiex-cracking agents are stannous alkylated catecholates in which the number of the carbon atoms in the alkyl substituent or substitu ents'is'atleast eight. T

The tendency of white side wall tires to-crack in use has retarded their adoption. Certain of the 'agentswhieh have been found to retard such cracking (called antiflex-crackingv agents) discolor the side walls. A satisfactory antiflexcracking agent for white side walls must be nondiscoloring.

stannous catecholate and the lower hydrocarbon-substituted derivatives, such as stannous dimethylcatecholate and stannous cyclohexylcatecholate, are inefiective as antifiex-cracking agents. However, the higher alkylated compounds have been found to be excellent antiflexcracking agents and are non-discoloring. Illustrative of the antiflex-cracking agents of this invention are:

Stannous di-tert.-butycatecholate Stannous octylcatecholate stannous octyl-4-methylcatecholate Stannous diamylcatecholate stannous nonylcatecholate Stannous heptyl-4-methylcatecholate stannous dodecylcatecholate Stannous dihexylcatecholate stannous decylcathecholate It appears that such higher alkyl substituents render these stannous catecholates more soluble in the natural rubber than the unalkylated or lower alkylated compounds and thus make the presence of the stannous compound efiective.

The following examples illustrate the production of the alkylated compounds:

EXAMPLE 1 stannous octylcatecholate Octylcatechol, 9.5 grams, was dissolved in methanol with 9.6 grams of stannous chloride hydrate. Into this solution with mechanical stirring were dropped 3.4 grams of sodium hydroxide in 125 ml. of 30 per cent aqueous methanol. An equal volume of water was added. The precipitate was filtered, washed with aqueous alcohol, and then water, and dried at 75 C. The yield was 13.3 grams.

EXAMPLE 2 stannous di-tertiary-butylcatecholate Di-tertiary-butylcatechol, 15.0 grams, and 15.1 grams of stannous chloride hydrate were dissolved in- 150' m1. of methanol. 'A 'solut i on of 5 35 grams of sodium hydroxide in 150" ml.flof 30 per cent methanol was dropped inwith stirring. Two 100 ml. portions of water were added. The precipitate was-filteredcwashed' with methanol and water, and dried- 4hours at C.- The yield was 21.3

grams. I

The stannous catecholates were compounded in a usual formula for white'side wiall' tires, asfollows:

Pale crepe rubber Wax Activator Stearic Acid" Stannous octylcatecholatc stannous di-tert.-butylcatecholate Flex Life Cracks per Hours Hour Sample A 51. 22 3. 1 Sample B 58. 38 2.6 Blank 39.60 7.5

The cracks per hour is the average rate of crack formation.

After natural weathering for 8 weeks and after 4 hours artificial weathering (carbon arcs, no filters), neither of the two stabilized materials nor the blank showed any discoloration.

The above examples are illustrative of the invention and are not to be interpreted as limiting the invention to the details given. Various compounding ingredients may be used, and it is not essential that a white pigment be employed or that the rubber be used in tires. The amount of antiflex-cracking agent employed may vary from about 0.5 up to about 8 parts per parts of rubber or more. Various changes in compounding and procedure, etc., may be made without departing from the scope of the invention which is defined in the appended claims.

What I claim is:

1. Natural rubber vulcanizate which contains as an antifiex-cracking agent a small amount of a stannous catecholate which is substituted with at least one alkyl substituent and the number of carbon atoms in the alkyl substituents of which totals at least eight.

2. White natural rubber vulcanizate pigmented with titanium dioxide which contains as an antia flex-cracking agent a small amount of a stannous catecholate which is substituted with at least one alkyl substituent and the number of carbon atoms in the alkyl substituents of which totals at least eight. v

3. White natural rubber pigmented'withv um nium dioxide which contains as an antiflex-crack- 1 rubber stock pigmented with titanium dioxide and containing as an antifiex-craoking agent a small amount of stannous octylcatecholate.

8. The process of producing white natural rubber vuicanizate which comprises curing natural rubber stock pigmented with titanium dioxide and containing as an'antiflex-cracking agent a small amount of stannous di-tertiary-butylcatecholate.

ing agent a small amount of stannous octyl- 1 catecholate.

4. White natural rubber pigmentedwith titanium dioxide which contains as an antifiex-cracking agent a small amount ofstannous iii-tertiarybutylcatecholate' 5'. The process of curing natural rubberwhich comprisescuring the same in the presence of a small amount of an antiflex-cracking agent which is a stannous catecholate which is substituted with at least one alkyl substituent and the number of carbon atoms in the alkyl substituents of which totals at least eight.

6. The process of producing white natural rubber vulcanizate which comprises curing natural JOSEPH C. AMBELANG.

REFERENQES CITED Thefollowing references are of record in the file ofthis patent: I

UNITED STATES PATENTS Number Name Date 2,310,449 Lightbown et a1. Feb, 9, 1943 2,334,470 Armstrong Nov. 16, 1943 2,335,089 Sibley Nov. 23, 1943 2,445,367 Robey et a1. July 20, 1948 FOREIGN PATENTS Number Country, Date 526,072 Great Britain Sept. 10, 194i) 

1. NATURAL RUBBER VULCANIZATE WHICH CONTAINS AS AN ANTIFLEX-CRACKING AGENT A SMALL AMOUNT OF A STANNOUS CATECHOLATE WHICH IS SUBSTITUTED WITH AT LEAST ONE ALKYL SUBSTITUENT AND THE NUMBER OF CARBON ATOMS IN THE ALKYL SUBSTITUENTS OF WHICH TOTALS AT LEAST EIGHT. 